// AES_Sbox is pre-computed multiplicative inverse in GF(2^8) used in SubBytes and KeyExpansion
var AES_Sbox =[	0x63,0x7c,0x77,0x7b,0xf2,0x6b,0x6f,0xc5,0x30,0x01,0x67,0x2b,0xfe,0xd7,0xab,0x76,
		0xca,0x82,0xc9,0x7d,0xfa,0x59,0x47,0xf0,0xad,0xd4,0xa2,0xaf,0x9c,0xa4,0x72,0xc0,
		0xb7,0xfd,0x93,0x26,0x36,0x3f,0xf7,0xcc,0x34,0xa5,0xe5,0xf1,0x71,0xd8,0x31,0x15,
		0x04,0xc7,0x23,0xc3,0x18,0x96,0x05,0x9a,0x07,0x12,0x80,0xe2,0xeb,0x27,0xb2,0x75,
		0x09,0x83,0x2c,0x1a,0x1b,0x6e,0x5a,0xa0,0x52,0x3b,0xd6,0xb3,0x29,0xe3,0x2f,0x84,
		0x53,0xd1,0x00,0xed,0x20,0xfc,0xb1,0x5b,0x6a,0xcb,0xbe,0x39,0x4a,0x4c,0x58,0xcf,
		0xd0,0xef,0xaa,0xfb,0x43,0x4d,0x33,0x85,0x45,0xf9,0x02,0x7f,0x50,0x3c,0x9f,0xa8,
		0x51,0xa3,0x40,0x8f,0x92,0x9d,0x38,0xf5,0xbc,0xb6,0xda,0x21,0x10,0xff,0xf3,0xd2,
		0xcd,0x0c,0x13,0xec,0x5f,0x97,0x44,0x17,0xc4,0xa7,0x7e,0x3d,0x64,0x5d,0x19,0x73,
		0x60,0x81,0x4f,0xdc,0x22,0x2a,0x90,0x88,0x46,0xee,0xb8,0x14,0xde,0x5e,0x0b,0xdb,
		0xe0,0x32,0x3a,0x0a,0x49,0x06,0x24,0x5c,0xc2,0xd3,0xac,0x62,0x91,0x95,0xe4,0x79,
		0xe7,0xc8,0x37,0x6d,0x8d,0xd5,0x4e,0xa9,0x6c,0x56,0xf4,0xea,0x65,0x7a,0xae,0x08,
		0xba,0x78,0x25,0x2e,0x1c,0xa6,0xb4,0xc6,0xe8,0xdd,0x74,0x1f,0x4b,0xbd,0x8b,0x8a,
		0x70,0x3e,0xb5,0x66,0x48,0x03,0xf6,0x0e,0x61,0x35,0x57,0xb9,0x86,0xc1,0x1d,0x9e,
		0xe1,0xf8,0x98,0x11,0x69,0xd9,0x8e,0x94,0x9b,0x1e,0x87,0xe9,0xce,0x55,0x28,0xdf,
		0x8c,0xa1,0x89,0x0d,0xbf,0xe6,0x42,0x68,0x41,0x99,0x2d,0x0f,0xb0,0x54,0xbb,0x16];

// Rcon is Round Constant used for the Key Expansion [1st col is 2^(r-1) in GF(2^8)]
var AES_Rcon = [[0x00, 0x00, 0x00, 0x00],
		[0x01, 0x00, 0x00, 0x00],
		[0x02, 0x00, 0x00, 0x00],
		[0x04, 0x00, 0x00, 0x00],
		[0x08, 0x00, 0x00, 0x00],
		[0x10, 0x00, 0x00, 0x00],
		[0x20, 0x00, 0x00, 0x00],
		[0x40, 0x00, 0x00, 0x00],
		[0x80, 0x00, 0x00, 0x00],
		[0x1b, 0x00, 0x00, 0x00],
		[0x36, 0x00, 0x00, 0x00] ]; 

/*
 * AESCipher function: use 'key' to encrypt 'input' with Rijndael algorithm
 *
 *   takes   byte-array 'input' (16 bytes)
 *           byte-array 'key' (16/24/32 bytes)
             2D byte-array key schedule 'w' (Nr+1 x Nb bytes)
 *   returns byte-array encrypted value (16 bytes)
 */

function AESCipher(input, key, w) {
  var Nk = key.length/4  // key length (in words)
  var Nr = Nk + 6;       // no of rounds
  var Nb = 4;            // block size: no of columns in state (fixed at 4 for AES)

  var state = [[],[],[],[]];  // initialise 4xNb byte-array 'state' with input
  for (var i=0; i<4*Nb; i++) state[i%4][Math.floor(i/4)] = input[i];

  state = AddRoundKey(state, w, 0, Nb);

  for (var round=1; round<Nr; round++) {
    state = SubBytes(state, Nb);
    state = ShiftRows(state, Nb);
    state = MixColumns(state, Nb);
    state = AddRoundKey(state, w, round, Nb);
  }

  state = SubBytes(state, Nb);
  state = ShiftRows(state, Nb);
  state = AddRoundKey(state, w, Nr, Nb);

  var output = new Array(4*Nb);  // convert to 1-d array before returning
  for (var i=0; i<4*Nb; i++) output[i] = state[i%4][Math.floor(i/4)];
  return output;
}

function SubBytes(s, Nb) {    // apply SBox to state S [§5.1.1]
  for (var r=0; r<4; r++) {
    for (var c=0; c<Nb; c++) s[r][c] = AES_Sbox[s[r][c]];
  }
  return s;
}

function ShiftRows(s, Nb) {    // shift row r of state S left by r bytes [§5.1.2]
  var t = new Array(4);
  for (var r=1; r<4; r++) {
    for (var c=0; c<4; c++) t[c] = s[r][(c+r)%Nb];  // shift into temp copy
    for (var c=0; c<4; c++) s[r][c] = t[c];         // and copy back
  }          // note that this will work for Nb=4,5,6, but not 7,8: see
  return s;  // fp.gladman.plus.com/cryptography_technology/rijndael/aes.spec.311.pdf 
}

function MixColumns(s, Nb) {   // combine bytes of each col of state S [§5.1.3]
  for (var c=0; c<4; c++) {
    var a = new Array(4);  // 'a' is a copy of the current column from 's'
    var b = new Array(4);  // 'b' is a{02} in GF(2^8)
    for (var i=0; i<4; i++) {
      a[i] = s[i][c];
      b[i] = s[i][c]&0x80 ? s[i][c]<<1 ^ 0x011b : s[i][c]<<1;
    }
    // a[n] ^ b[n] is a{03} in GF(2^8)
    s[0][c] = b[0] ^ a[1] ^ b[1] ^ a[2] ^ a[3]; // 2*a0 + 3*a1 + a2 + a3
    s[1][c] = a[0] ^ b[1] ^ a[2] ^ b[2] ^ a[3]; // a0 * 2*a1 + 3*a2 + a3
    s[2][c] = a[0] ^ a[1] ^ b[2] ^ a[3] ^ b[3]; // a0 + a1 + 2*a2 + 3*a3
    s[3][c] = a[0] ^ b[0] ^ a[1] ^ a[2] ^ b[3]; // 3*a0 + a1 + a2 + 2*a3
  }
  return s;
}

function AddRoundKey(state, w, rnd, Nb) {  // xor Round Key into state S [§5.1.4]
  for (var r=0; r<4; r++) {
    for (var c=0; c<Nb; c++) state[r][c] ^= w[rnd*4+c][r];
  }
  return state;
}

function KeyExpansion(key) {  // generate Key Schedule (byte-array Nr+1 x Nb) from Key [§5.2]
  var Nk = key.length/4  // key length (in words)
  var Nr = Nk + 6;       // no of rounds
  var Nb = 4;            // block size: no of columns in state (fixed at 4 for AES)

  var w = new Array(Nb*(Nr+1));
  var temp = new Array(4);

  for (var i=0; i<Nk; i++) {
    var r = [key[4*i], key[4*i+1], key[4*i+2], key[4*i+3]];
    w[i] = r;
  }

  for (var i=Nk; i<(Nb*(Nr+1)); i++) {
    w[i] = new Array(4);
    for (var t=0; t<4; t++) temp[t] = w[i-1][t];
    if (i % Nk == 0) {
      temp = SubWord(RotWord(temp));
      for (var t=0; t<4; t++) temp[t] ^= AES_Rcon[i/Nk][t];
    } else if (Nk > 6 && i%Nk == 4) {
      temp = SubWord(temp);
    }
    for (var t=0; t<4; t++) w[i][t] = w[i-Nk][t] ^ temp[t];
  }

  return w;
}

function SubWord(w) {    // apply SBox to 4-byte word w
  for (var i=0; i<4; i++) w[i] = AES_Sbox[w[i]];
  return w;
}

function RotWord(w) {    // rotate 4-byte word w left by one byte
  w[4] = w[0];
  for (var i=0; i<4; i++) w[i] = w[i+1];
  return w;
}

// Counter mode compatible with Crypt::Rijndael perl module

var AES_KEYSIZE = 32;
var AES_KEY = new Array(AES_KEYSIZE);

function gen_key(password) {
	var pw_sha = str_sha256(password);
	for (var i=0; i<AES_KEYSIZE; i++) AES_KEY[i] = pw_sha.charCodeAt(i);
}

var AES_BLKSIZE = 16;
var AES_CTR = new Array(AES_BLKSIZE);

function inc_counter() {
	for (var i=AES_BLKSIZE-1; i>=0; i--) {
		if (AES_CTR[i] < 0xff) {
			AES_CTR[i]++;
			return;
		}
		AES_CTR[i] = 0;
	}
	return;
}

/* - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -  */

/* 
 * Use AES to encrypt 'plaintext' with 'password' in 'Counter' mode of operation
 *                    - see http://csrc.nist.gov/publications/nistpubs/800-38a/sp800-38a.pdf
 *   for each block
 *   - outputblock = cipher(counter, key)
 *   - cipherblock = plaintext xor outputblock
 */
function CTR_AES_encrypt(plaintext, password) {
  	gen_key(password);
	// generate key schedule - an expansion of the key into distinct Key Rounds for each round
	var keySchedule = KeyExpansion(AES_KEY);

	// initialise counter block (NIST SP800-38A §B.2)
	var ciphertext = str_sha256(''+(new Date()).getTime()+Math.random()+Math.random()).substr(0, AES_BLKSIZE);
	for (var i=0; i<AES_BLKSIZE; i++) AES_CTR[i] = ciphertext.charCodeAt(i);

	// pad the plaintext
	var pad_len = AES_BLKSIZE - plaintext.length % AES_BLKSIZE;
	for (var i=0; i<pad_len-1; i++) plaintext += "\0";
	plaintext += String.fromCharCode(pad_len);
	var blockCount = plaintext.length/AES_BLKSIZE;
	for (var b=0; b<blockCount; b++) {
		// encrypt counter block
		var cipherCntr = AESCipher(AES_CTR, AES_KEY, keySchedule);
		for (var i=0; i<AES_BLKSIZE; i++) { // xor plaintext with ciphered counter byte-by-byte
			var plaintextByte = plaintext.charCodeAt(b*AES_BLKSIZE+i);
			var cipherByte = plaintextByte ^ cipherCntr[i];
			ciphertext += String.fromCharCode(cipherByte);
		}
		inc_counter();
	}
	return ciphertext;
}


/* 
 * Use AES to decrypt 'ciphertext' with 'password', in Counter mode of operation
 *
 *   for each block
 *   - outputblock = cipher(counter, key)
 *   - cipherblock = plaintext xor outputblock
 */
function CTR_AES_decrypt(ciphertext, password) {
	gen_key(password);
	var keySchedule = KeyExpansion(AES_KEY);
	// recover init counter from ciphertext
	for (var i=0; i<AES_BLKSIZE; i++) AES_CTR[i] = ciphertext.charCodeAt(i);
	var blockCount = ciphertext.length/AES_BLKSIZE - 1;
	var plaintext = '';
	for (var b=0; b<blockCount; b++) {
		// encrypt counter block
		var cipherCntr = AESCipher(AES_CTR, AES_KEY, keySchedule);
		for (var i=0; i<AES_BLKSIZE; i++) {
			var ciphertextByte = ciphertext.charCodeAt((1+b)*AES_BLKSIZE+i);
			var plaintextByte = ciphertextByte ^ cipherCntr[i];
			plaintext += String.fromCharCode(plaintextByte);
		}
		inc_counter();
	}
	var plain_len = plaintext.length;
	var pad_len = plaintext.charCodeAt(plain_len-1);
	return plaintext.substr(0, plain_len - pad_len);
}
